Add button to custom subform

Hi,
  I am just getting into setting up some cutomized features to expand the functionality within projects.  I am hoping someone can help me and stop me going round in circles for a third time today....:h_a_w:

I have created a custom record (to keep track of engineering samples) which appear as a sublist on a custom subtab on the project form.

I would like to have a button on the subform, to create a new sample parts record entry for that project.  The sublist displayes correctly, but there are no buttons above it as there are with "user notes" etc.  Is this because I haven't set the sublist up correctly, or do I need to do this in suitescript?  If sI need to create a script, I assume that this would be client side script attached to the form, but I can't see how to relate th script to the custom subtab.